Affiliations: [a] School of Allied Health, Murdoch University, Perth, WA, Australia
| [b] Faculty of Allied Health and Wellbeing, University of Central Lancashire (UCLan), Preston, UK
| [c] Eastern Health, Victoria, Box Hill, VIC, Australia
| [d] School of Health, University of the Sunshine Coast (UniSC), Sippy Downs, QLD, Australia
Correspondence:
[*]
Address for correspondence: Lee Daffin, School of Allied Health, Murdoch University, Perth, WA, Australia.
E-mail: Lee.Daffin@murdoch.edu.au.
Abstract: BACKGROUND:Modifying the horizontal position of the load in a backpack will change the size of the external torque it creates on the wearer but the effect on postural stability is unclear. OBJECTIVE:To determine if changing the horizontal position of a fixed backpack load affects postural stability in young adults. METHODS:A backpack was attached to a steel frame with a bar protruding posteriorly. A fixed load (5% body mass) was placed at three distances along the bar – 0 m, 0.20 m, and 0.40 m. Centre of pressure (CoP) derived measurements were recorded from a force platform sampling at 100 Hz. For each condition participants performed three 90s narrow stance trials with their eyes closed whilst standing on a firm surface. A comparison was made across unloaded (no backpack) and loaded conditions. RESULTS:There was an immediate decrease in postural stability when a loaded backpack was worn. Only two of the CoP derived measures (Total Excursion - TEx, and Mean Velocity Total Excursion - MVel TEx) differed between the loaded at 0.20 m and loaded at 0 m conditions. All CoP derived measures differed between the loaded at 0.40 m and loaded at 0 m conditions. Furthermore, three of the CoP derived measures (Anterior/Posterior Root Mean Square - A/P RMSq, TEx, and MVel TEx) differed between the loaded at 0.40 m and loaded at 0.20 m conditions. CONCLUSION:The distribution of a load within a backpack must be carefully considered. The findings for the 0.40 m condition are important for the use and design of large backpacks used by multi-day hikers, travellers, and the military.
